Dimming control of lighting is desirable in order to provide adjustment of light levels and to reduce energy consumption. Prior art designs for LED drivers that provide dimming typically include control integrated circuits specially designed to provide dimming or require elevated circuit complexity and cost to accomplish dimming, including for example, to accommodate dimming via a control signal or TRIAC control of the AC supply.
Transformer coupled switching regulators are often used as LED driver circuits. One such type of driver circuit typically used for higher power LED lighting applications is a flyback converter, which achieves a relatively high level of efficiency. For dimming the average current supplied to the LEDs must be decreased. For example, the average current can be reduced by providing pulse width modulation (PWM); however, this can be difficult in a flyback converter, thus limiting the practical range of dimming available.
A flyback converter utilizing a power factor correction (PFC) controller, for example, a current-mode PFC controller operating in transition mode, provides an isolated, low cost, low component count supply to LEDs. Flyback converters with a PFC controller are especially advantageous with higher power LEDs to maintain high efficiency and reduce distortion of the supply line current. While such a driver circuit can be designed to efficiently provides a constant current for a specific LED load, providing dimming control by decreasing the current supplied by a constant current supply generally adds much more complexity and cost to the circuit.
It is therefore desirable to provide dimming control of an LED driver circuit utilizing a current-mode PFC controller without having to add expensive circuit components or complexity that increase the cost of implementing typical driver control configuration disclosed in the prior art.